Method of evacuating and sealing a double-walled container



METHOD OF EVACUATING AND SEALING A DOUBLE-WALLED conwuman Filed Aug. 5,. 1966 51 "-5: 16 a l 3 iii: '5 I II FIG. 2 i 26 I l GETTER VACUUM 10E EIZO,

DONALD E. 8080 Y v ATT'YS United States Patent Ofi ice 3 423 817 METHOD OF EVACIJATING AND SEALING A DOUBLE-WALLET) CONTAINER Donald E. Hobo, 2217 N. Auburn, Indianapolis, Ind. 46224 Filed Aug. 3, 1966, Ser. No. 570,037 US. Cl. 29421 Int. Cl. B651) 55/00, 31/02; B23p 15/00 This invention relates to a method of evacuating and sealing a double-walled container and, more particularly, to an improved method of forming a vacuum-insulated container in which a getter material is sealed within the evacuated space.

As it is well known, getter materials such as metallic barium are commonly used in the air-evacuated spaces of double-walled containers in order to absorb or combine with traces of gas which might otherwise greatly reduce the effectiveness of the evacuated space as thermal insulation. Since metallic barium combines readily with oxygen and other gases, it is essential that it be protected against contact with air prior to its introduction into the evacuated space; otherwise it will be rendered ineffective as a getter before it is in position to perform a useful gettering function.

In the past, it has been considered necessary to encapsule the barium to protect it against exposure until after it is in place within the evacuated space of a vacuum-insulated vessel. Normally, a capsule containing such barium is securely attached to the inner surface of a section of the outer shell adjacent the evacuation opening before the two sections of the outer shell are welded or otherwise secured together. Thereafter, the sections of the outer shell are joined, the space between the inner and outer shell is evacuated and, finally, the capsule is ruptured (usually by a pin at the inner end of the closure plug) to expose the barium within the containers evacuated space and the evacuation opening is sealed.

While the encapsulating method protects the barium against exposure, it is relatively expensive and has the inherent disadvantage of tending to confine rather than distribute the barium throughout the evacuated space. Once the capsule has ruptured (and it may be extremely difficult to ascertain that such rupture has in fact taken place), the barium tends to remain as a mass in substantially the same area and considerable agitation of the sealed container may be necessary before even a limited distribution of the barium within the sealed space is achieved. The mean free path of gas molecules at the desired vacuum pressure (below 0.1 micron of mercury) is long enough that gas molecules have difficulty in penetrating a confined mass of getter powder. Accordingly, a confined mass of getter exhibits an extremely low gettering rate in comparison to a similar mass that is widely dispersed. Furthermore, such a method requires some means for locating the capsule and fracturing it after the insulating space has been evacuated, and for determining that fracturing has in fact occurred, problems which find solutions only through the use of relatively expensive procedures and equipment.

Accordingly, it is an object of the present invention to provide an improved method for introducing a getter ma terial into the evacuated space of an insulated doublewalled container, thereby overcoming the aforementioned defects and disadvantages of prior practices. Specifically, it is an object to provide a method in which a finely-divided getter material such as metallic barium, barium oxide or lanthanum oxide may be introduced into the inter-wall cavity of a container in a relatively non-confined manner, thereby increasing the exposed surface area of the getter and its efficiency and effectiveness as a gas-withdrawing agent. A further object is to provide an improved method for introducing a gettering agent into the inter-wall space of a vacuum-insulated con- Claims 3,423,817 Patented Jan. 28, 1969 tainer without the involvement and sulation.

Another object is to provide an improved method for evacuating and sealing a double-walled insulated container. In this connection, it is a specific object to provide a method which dispenses with drilling or punching an evacuation port, with machining and securing a threaded fitting or boss to a container about an evacuation port, and with providing a plug structure of the type commonly utilized for sealing an evacuation port, all of which are relatively expensive and time-consuming procedures which have been considered necessary in the past in order to evacuate the inter-wall cavity of a double-walled container and for sealing that cavity after a barium capsule has been introduced therein and the inter-Wall space has been fully evacuated.

Other objects will appear from the specification and drawings in which:

FIGURE 1 is a side elevational view shown partly in section and illustrating a double-walled container at an intermediate stage in its fabrication;

FIGURE 2 is a somewhat diagrammatic broken sectional view illustrating a subsequent step in the fabrication of a vacuum-insulated vessel;

FIGURE 3 is a broken elevational view shown partly in section and illustrating the container with its interwall space fully sealed.

Referring to the drawings, FIGURE 1 illustrates a container 10 composed of an inner shell 11, an outer shell 12, and a neck tube 13 projecting upwardly from the inner shell. In the illustration given, the neck tube is formed as a separate part and is permanently secured to an annular collar 14 provided by the inner shell; however, it will be understood that the neck tube and inner shell might be formed integrally under certain circumstances as, for example, where both parts are formed of the same gas-impermeable plastic material. It is important that the neck tube be formed of a material having low thermal conductivity, and one which is also gas impermeable and of high strength. Plastic materials, such as epoxy resins impregnating a glass fiber matrix have been found particularly effective, and other plastic materials such as polycarbonates, acrylonitirile-butadienestyrene copolymers, and acetal resins may also be used. Gas impermeability of the neck tube is achieved by coating or lining the tube with a metallic liner or film which, if desired, may be electroplated directly upon the plastic.

Except for the upwardly-extending opening defined by the neck tube, the inner shell 11 is completely closed. Outer shell 12 is concentric with the inner shell and is sufficiently larger than the inner shell to define an insulating space 15 between the opposing surfaces of the respective parts. A suitable insulating material 16 such as glass fibers or laminates of fibrous materials and reflective metal films is provided in space 15 to increase the thermal insulating properties and to provide a support for the inner shell 11 within outer shell 12.

The shells may be formed of aluminum or any other suitable material and, if necessary, the bottom wall 12a of the outer shell may be formed as a separate piece and then welded or otherwise secured in place after the inner shell 11 has been concentrically positioned as shown.

The outer shell is provided with upstanding neck 12b which is concentric with neck tube 13 and which is sufficiently larger than the neck tube to define an annular evacuation port or passage 17 therebetween. The outer surface of the neck tube 13 in the vicinity of neck 12b is circumferentially grooved at 18 and is covered with a relatively soft sealing material. The sealing element 19 may also be formed of other nonvolatile materials having low gas permeability such as synthetic rubbers (for ex expense of encapample, butadiene-nitrile polymers), or relatively soft metals such as lead.

FIGURE 2 illustrates somewhat diagrammatically the structure involved in evacuating the insulating space 15, for introducing metallic barium or other suitable gas-reactive material therein, and for closing passage 17 to form the sealed container illustrated in FIGURE 3. "the apparatus includes a casing 20 defining a vacuum chamber 21 therein. A vacuum pump 22 is adapted to communicate with the chamber through passage 23, and a two-position valve 24 interposed along line 23 may be selectively positioned to place the chamber 21 in communication with either the pump 22 or with the atmosphere.

The container is rotatably supported within chamber 21 for rotation about its vertical axis and in the wall of the casing above the container is a feed tube 25 for the introduction of a suitable getter material in a finelydivided state. Metallic barium in a powdered state is particularly suitable as a getter material and is therefore specifically mentioned in the following specification; however, it is to be understood that other finely-divided getter materials such as barium oxide, lanthanum oxide, palladium oxide, and misch metal may also be used. Tube 25 communicates at its lower end with the chamber 21 and at its upper end with a barium container 26. Valve 27 in line 25 is normally closed and maintains container 26 in hermetically-sealed condition, thereby protecting the powdered barium against exposure to reactive gases.

Beneath feed tube 25 is a hopper 28 for directing barium from the feed tube into the annular passage 17 between neck tube 13 and neck 12!). It will be observed that rotation of the container 10 about its axis will not shift the hopper and annular evacuation passage out of alignment because of the coaxial relationship of neck 12b and neck tube 13.

About the sides of neck 1211 within chamber 21 are a plurality of wheels or rollers 29 carried by vertical shafts 30 and arms 31. The arms or jaws 31 support the rollers for inward movement in the directions indicated by arrows 32, and such rollers may be power driven for rotation about the axes of shafts 30 by any conventional driving means (not shown). As shown in FIGURE 2, the peripheral surfaces of the rollers are provided with circumferential ribs which are in horizontal register with the circumferential grooves 18 in neck tube 13.

In the operation of the apparatus, container 10 is first placed within chamber 21 and vacuum pump 22 is then activated to withdraw air or other gases from the chamber and from space 15. After substantially all of the gaseous material has been Withdrawn therefrom, valve 27 is shifted into an open position and a selected amount of finelydivided barium, or any other suitable getter material, is released from container 26, passes into hopper 28, and finally into space 15. The barium is thereby distributed in a relatively unconfined state, the powder simply being scattered upon and into the fibrous insulating material 16 within space 15. By rotating the container 10 about its vertical axis at the time the barium is introduced, the extent of distribution of the barium is further increased.

Thereafter, while chamber 21 is still in an evacuated condition, rollers 33 are urged inwardly into compressing engagement with neck 12!) and, upon rotation of the container, spin the neck inwardy until its inner surface seats tightly against the covered or coated outer surface of neck tube 13 (FIGURE 3). If desired, a mandrel may be disposed within the neck tube to prevent deformation of the neck tube as neck 12b is spun inwardly. The sealing material 19 which, as previously described, may be polymerized tetrafluoroethylene or any other substantially impermeable material (i.e., has a vapor pressure of less than 0.1 micron of mercury) is restrained against cold flowing by circumferential grooves 18 and forms a hermetic seal between the inner and outer shells. Thus, in its completed condition, the container assumes the appearance illustrated in FIGURE 3. Rollers 29 are retracted into the positions 4 illustrated in FIGURE 2, valve 24 is opened to admit air into chamber 21, and the completed container 10 is withdrawn from the evacuation chamber.

While in the foregoing I have disclosed the method of the present invention in considerable detail for purposes of illustration, it will be understood by those skilled in the art that many of these details may be varied without departing from the spirit and scope of the invention.

I claim:

1. In a method of evacuating and sealing a space between inner and outer shells of a double-walled container, the inner shell having an upstanding neck tube and the outer shell being of formable material and having an enlarged neck defining an annular passage about said neck tube, the steps comprising: evacuating gas from the space between said inner and outer shells by withdrawing it through said annular passage; introducing a quantity of a finely-divided getter material into said space through said passage after the gas has been evacuated from sai dspace; and then deforming said neck of said outer shell inwardly into sealing contact with said neck tube to seal the evacuated space between said shells.

2. The method of claim 1 in which there is the additional step of interposing a substantially impermeable sealant material between said neck tube and said neck prior to said step of deforming said neck.

3. In a method of forming a vacuum-insulated container, the steps of: forming a double-walled container having an inner shell with a neck tube atlixed thereto and an outer shell with a deformable neck spaced outwardly from said neck tube to define an annular passage there between; evacuating gas from the space between said inner and outer shells by withdrawing it through said pas sage; introducing a quantity of a finely-divided getter material into said space through said passage after gas has been evacuated from said space; and then deforming said neck of said outer shell inwardly into sealing contact with said neck tube to seal the evacuated space between said shells.

4. The method of claim 3 in which there is the aditional step of interposing a substantially impermeable sealant material between said neck tube and said neck prior to said step of deforming said neck.

5. The method of claim 4 in which said sealant material has a vapor pressure of no greater than 0.1 micron of mercury at approximately room temperature.

6. In a method of forming a vacuum-insulated container, the steps comprising: positioning a double-walled container in a vacuum chamber; evacuating gas from said chamber and from a space between the walls of said double-walled container through an opening therein; introducing into said space through said opening a finelydivided gas-gettering material while said container is disposed in said evacuated chamber; and thereafter sealing said opening while said container is disposed within said evacuated chamber.

7. The method of claim 6 in which said opening comprises an annular neck passage between the inner and outer walls of said container, and said step of sealing said opening comprises deforming said outer shell inwardly into sealing engagement with said inner shell to close said neck passage.

8. The method of claim 7 in which a sealant is interposed in said neck passage prior to said sealing step.

9. In a method of evacuating and sealing a space between the inner and outer shells of a double-walled container, the inner shell having an upstanding neck tube and the outer shell being of deformable material and having an enlarged neck defining an annular passage about said neck tube, the steps comprising: evacuating gas from the space between said inner and outer shells by withdrawing it through said annular passage; and then deforming said neck of said outer shell inwardly into sealing engagement with said neck tube to seal the evacuated space between said shells.

5 10. The method of claim 9 in which there is the additional step of interposing a deformable and substantially impermeable sealant material between said neck tube and said neck prior to the step of deforming said neck.

References Cited UNITED STATES PATENTS 6 3,055,101 9/1962 Bergan 29455 2,666,979 1/1954 Van Dusen 29421 TRAVIS S. McGEHEE, Primary Examiner.

HORACE M. CULVER, Assistant Examiner.

US. Cl. X.R. 

9. IN A METHOD OF EVACUATING AND SEALING A SPACE BETWEEN THE INNER AND OUTER SHELLS OF A DOUBLE-WALLED CONTAINER, THE INNER SHELL HAVING AN UPSTANDING NECK TUBE AND THE OUTER SHELL BEING OF DEFORMABLE MATERIAL AND HAVING AN ENLARGED NECK DEFINING AN ANNULAR PASSAGE ABOUT SAID NECK TUBE, THE STEPS COMPRISING: EVACUATING GAS FROM THE SPACE BETWEEN SAID INNER AND OUTER SHELLS BY WITHDRAWING IT THROUGH SAID ANNULAR PASSAGE; AND THEN DEFORMING SAID NECK OF SAID OUTER SHELL INWARDLY INTO SEALING ENGAGEMENT WITH SAID NECK TUBE TO SEAL THE EVACUATED SPACE BETWEEN SAID SHELLS. 